THE PRINCIPLES OF CINEMATOGRAPHY
For complete success in moving-picture work it is essential to have an
elementary knowledge of the principles upon which the art is based.
Although pictures are said to be shown in motion upon the screen, no
action is reproduced as a matter of fact. The eye imagines that it sees
movement. Each picture is an isolated snap-shot taken in the fraction
of a second. In projection upon the screen, however, the images follow
so rapidly one after the other and each remains in sight for so brief a
period that the successive views dissolve into one another. The missing
parts of the motion--the parts lost while the lens is closed between
the taking of each two pictures--are not detected by the eye. The
latter imagines that it sees the whole of the process of displacement
in the moving objects. In fact it sees only one-half--the half that
occurred in those fractions of seconds during which the lens was
open. What occurred while the lens was shut is not recorded. Animated
photography, therefore, is an optical illusion purely and simply.
The fact that an appearance of natural movement is seen under these
conditions is due to a physiological phenomenon which, for the want
of a better explanation, is termed "persistence of vision." This
peculiarity of the eye and brain remains a scientific puzzle, and
although in one or two quarters the theory of visual persistence is
ridiculed, the iconoclasts have not yet brought conclusive testimony to
upset it. The whole subject of persistence of vision in its relation
to moving-pictures is discussed at length by the present writer in
a former book to which he would refer such readers as may wish for
information on this subject.[1]
[1] See "Moving Pictures: How they are made and worked," Chapter I.
[Illustration: OPERATOR AND HIS CAMERA BURIED IN A HOLE TO TAKE
MOVING-PICTURES OF SMALL ANIMALS.]
[Illustration:
_By permission of the Motograph Co._
MAKING MOVING-PICTURES OF WILD RABBITS.
Mr. Frank Newman with his camera concealed in the bushes.]
[Illustration:
_From the "Cinema College," by permission of the Motograph Co._
THE NEST, SHOWING CURIOUS SUSPENSION BY FOUR STRINGS.
A UNIQUE PICTURE. THE MOTHER KING REGULUS FEEDING HER YOUNG.
Motion-pictures of the Golden-crested Wren, the smallest bird in the
British Isles.]
The eye is about one million times faster than the most rapid
sensitized emulsion which chemists have yet produced. So there is
nothing wrong about the popular opinion that the organ of sight is
the quickest of the senses. Yet it is not so quick that it cannot
be deceived. If the pictures of a cinematograph are projected upon
the screen at the rate of so many per second, the effect upon the
eye is that of perfectly natural movement. The laws that govern this
illusion have been discovered in a very interesting way. A positive
film was prepared, but between each successive image a wide white
line was inscribed. This film was then passed through the projector,
and the pictures were thrown upon the screen at the speed generally
accepted as being necessary to convey the effect of natural movement;
but animation could not be produced at all, however rapidly the
pictures were projected. The reason was simple. Immediately after a
picture disappeared from the screen the white flash occurred, and
notwithstanding its instantaneous character it was sufficient to wipe
out the image of the picture, which without the white line would have
lingered in the brain. Even when the pictures were run through the
projector at thirty per second, no impression of rhythmic movement
was obtained; they appeared in the form of still-life pictures with
spasmodic jumps from one to the other. They failed to blend or dissolve
in the brain, notwithstanding that the white flash in some cases was
only about one ten thousandth part of a second in duration.
Another film of the same subject then was passed through the projector
under conditions exactly similar except that the line dividing the
pictures in this case was black instead of white. When this picture
was thrown upon the screen, animation became apparent directly the
speed attained sixteen pictures per second, because after one image
had vanished from the screen it persisted in the brain, in spite of
the black flash, until the next picture appeared. Thus, the requisite
dissolving effect was obtained. The black flash did indeed produce a
defect like that which was common in the early days of cinematography
and was characterised generally as "flicker." But it did not suffice to
ruin the illusion of movement. A white flash destroys apparent motion,
owing to the brain being extremely sensitive to white: a black flash of
equal duration exercises no ill effects.
In the latest development of the art, one inventor has taken advantage
of this peculiarity. He has perfected a practical system wherewith the
shutter of the camera may be abandoned because each picture is cut off
from its neighbour by a very thin black line. An improved mechanism
jerks each picture off and brings the next one on the screen very
sharply, so that an effect is produced like that obtainable with the
shutter and without any impression of flicker. It may be pointed out
that with this invention there are none of the aberrations described in
a later chapter, such as the spokes of a wheel appearing to move in the
reverse direction to which the rim is travelling.
The next question is that of the speed at which it is necessary to
take and to project the pictures in order to get an apparently true
impression of natural movement. This factor to-day is governed almost
entirely by commercial considerations. It has been found, as a result
of elaborate investigation, that a speed of twelve to sixteen pictures
per second is the minimum wherewith in monochrome pictures animation is
obtainable. But this applies only to general work, such as records of
ordinary scenes, topical events and stage plays, where the action of
the moving objects is comparatively slow. In these instances an average
of sixteen pictures per second in photographing and projecting gives
completely satisfactory effects.
But in reality the speed is a variable quantity: it must be adapted
to the subject and the character of the work in hand. In other words,
strictly speaking, the speed must be accommodated to the velocity
of the subject so far as photographing is concerned, and also, in a
lesser degree, to the distance of the moving object from the lens. For
instance, when a man, walking four miles an hour, is photographed at
sixteen pictures per second, the movements recorded are far from being
natural or rhythmic. On the screen he appears to walk with a disjointed
action. To obtain a lifelike result, his pace should be slowed down
75 per cent., or the photographing speed should be accelerated to
seventy pictures per second at the least. This fact is illustrated very
conclusively in pictures of soldiers marching: they appear to advance
like automatons. Again, in photographing animals, a complete movement
is often lost between successive pictures. A cat in one picture will
be seen to the right; in the next picture it is on the left, having
sprung from one side to the other during the brief interval the lens
was closed. When extremely rapid movements have to be recorded, the
photographing speed has to be accelerated to an extreme degree, up
to ten thousand pictures or more per second in the case of a bullet
leaving the muzzle of a rifle, and up to two thousand pictures per
second to catch the movements of a dragonfly's wings. On the other
hand, in photographing very slow movements like the growth of a plant,
one picture per hour may be adequate.
In projection the speed can be adjusted. The ten thousand pictures per
second may be decelerated to sixteen per second to allow the movement
to be followed, and although the rifle bullet may appear to crawl
through the air, the movement is perfectly correct. Similarly the very
slow motions must be accelerated to sixteen pictures per second to
obtain evident animation. These two extreme phases of cinematographic
investigation are described at length in another part of this volume,
but are mentioned here merely to show that the photographing speed is
a somewhat elastic factor, to be adapted to circumstances in order to
produce passably natural effects.
For everyday work, however, a speed of sixteen pictures per second is
sufficient and represents the generally practised velocity. Possibly in
the near future the speed will be accelerated to twenty, twenty-two,
or twenty-four pictures per second, as the present speed is generally
admitted to be too slow. The eyes of the regular picture palace
patrons have become trained, as it were, with the result that there
is an appreciable strain of the eyes, while the disjointed character
of the movements on the screen may be detected. But when the taking
and projecting speed is accelerated by 50 per cent. the picture
stands steadier upon the screen, the movements are more natural,
and there is an entire absence of that automaton effect which is so
characteristic of most pictures taken under prevailing conditions.
These considerations do not affect photo-plays produced in the studio
so materially, because there the actions of the players can be slowed
down to suit the conditions.
One of the leading manufacturers is earnestly considering the
advisability of accelerating the taking and projecting speeds up
to about twenty pictures per second, and private investigations
and experiments have certainly demonstrated the value of such an
improvement. Unfortunately two difficulties prevent its immediate
realisation. An increase of only four pictures per second represents an
increase of 25 per cent. in the consumption of the film, and therefore
in its cost. The other difficulty is more serious. Existing apparatus,
both cameras and projectors, are geared to eight pictures per turn
of the handle. This involves two complete revolutions per second.
Consequently the gearing of the mechanism would have to be altered,
and this is a more troublesome question than appears at first sight.
Some time may elapse before a forward step is taken in this direction.
In matters of this character the cinematograph industry is notoriously
conservative, although the moment one firm courageously adopts an
accelerated speed, the higher quality of the resulting pictures will
force the others to follow the example.
As a matter of fact the decision to adopt sixteen pictures per second
was taken somewhat haphazardly without any scientific investigation.
When it became standardised, film was expensive. Accordingly, efforts
were made to secure the requisite effect with the minimum expenditure
of film. Machines were built to coincide with these requirements,
and the original designs have been followed slavishly in their broad
outlines ever since.